(Adds U.S. to double jets on NATO patrol in Balkans, Dempsey comments, background)

By Phil Stewart and David Alexander

WASHINGTON, March 5 (Reuters) - The Pentagon will more than double the number of U.S. fighter jets on a NATO air patrol mission in the Baltics and do more training with Poland's air force as it strives to reassure allies alarmed by the crisis in Ukraine, officials said on Wednesday.

General Martin Dempsey, chairman of the Joint Chiefs of Staff, told a Senate hearing that he had directed the U.S. military's European Command to "consult and plan within the construct of the North Atlantic Council" while stressing the intent was to help stabilize the situation in Ukraine.

"Obviously we want to provide NATO's leaders with options that stabilize and not escalate tensions in the Ukraine," Dempsey said.

The United States has shown no interest in pursuing military options in the dispute with Russia over the Crimea, but it has taken other actions, such as cutting off military exchanges with Russia on Monday.

Dempsey said he spoke with his Russian counterpart on Wednesday and urged restraint in the days ahead "in order to preserve room for a diplomatic solution."

Russia and the West are locked in their most serious confrontation since the end of the Cold War.

Centered on influence in Ukraine, a former Soviet republic with historic ties to Moscow, the crisis has worsened daily since President Viktor Yanukovich was ousted on February 22 amid protests over his decision to quash a trade deal with the European Union.

A strategic link between East and West, Ukraine is also a major commodities exporter.

Ukraine has said that Crimea is now occupied by Russia, which has a base there for its Black Sea fleet.

After Yanukovich's ouster, Russia effectively occupied Ukraine's Crimea region. This has raised international tensions and fears of war and a punishing decline on Monday in Russia's rouble and stock market.

Moscow has asserted that troops that have seized control of the Black Sea peninsula are not under its command but are militia. These assertions have been ridiculed by the West.

"My military judgment is these are soldiers who have been taken out of their traditional uniforms, re-purposed for placement in the Crimea as a militia force," Dempsey said, adding that although he did not have evidence at this time he believed such evidence would likely become available.

JETS ON PATROL

Defense Secretary Chuck Hagel said the United States would step up its participation in NATO's 10-year-old air policing missions over the Baltic states of Estonia, Latvia and Lithuania. The duties rotate among NATO members.

The United States took over air policing duties from Belgium in January, providing four F-15 aircraft through May. The jets are on call to respond to any violations of Baltic airspace.

One U.S. defense official, speaking on condition of anonymity, said the Pentagon would send six additional F-15 jets and one KC-135 refueling aircraft this week to augment the mission.

A second U.S. defense official said there were about 10 U.S. Air Force personnel in Poland to support rotations of U.S. aircraft, including F-16 fighter jets, for training.

Hagel said the United States would boost training with Poland's air force.

"Across the administration, our efforts ... (are) focused on de-escalating crisis, supporting the new Ukrainian government with economic assistance and reaffirming our commitments to allies in Central and Eastern Europe," Hagel said.

It was unclear how the United States would increase training but one option would be to do more of it or to open training to regional allies, both U.S. defense officials said. (Reporting by Phil Stewart and David Alexander; Editing by Andrew Hay, Toni Reinhold)